Hi Beer-belly - caulis are greedy, thirsty, and fussy b*gg*rs into the bargain. Any check to their growth, and they throw a hissy fit. I find them very hard to grow well, and hard to trace back what I've done wrong.
Some thoughts - soil not rich enough at the beginning? Or not getting fed as they grow? Or running short on water at some point?
Or, probably most likely, you're not talking to them sweetly enough - remember the day of the famous hangover? They're getting their own back! :)
All best - Gavin